When alleged Al Qaeda sympathizer Jose Padilla landed in Chicago in May 2002, he was met by federal agents armed with a warrant authorizing them to take him into custody.

To obtain their warrant, the agents told a federal judge that two weeks earlier a confidential source had revealed that Mr. Padilla was plotting to build and detonate a radiological "dirty" bomb in the United States.

What the agents did not tell the judge is that their "confidential source" was not speaking voluntarily. His information had been obtained in controversial interrogation sessions at a secret Central Intelligence Agency prison overseas.

The confidential source was a man named Zayn Abu Zubaydah, the same individual identified last week by President Bush as the first Al Qaeda suspect subjected to harsh interrogation tactics by US officials.

"We knew that Zubaydah had more information that could save innocent lives, but he stopped talking," the president said in a speech on Sept. 6. "So the CIA used an alternative set of procedures."

In 2002, the agency's pressing goal was intelligence-gathering to disrupt possible terror attacks rather than a law- enforcement operation to gather evidence that might be used against American citizens in American courts. But now, four years later, the information from those harsh interrogation sessions conducted by or at the behest of the CIA is playing an important role in government efforts to convict Padilla in a terror conspiracy case in Miami.

The case is emerging as a major test of whether such intelligence information is admissible in US courts. And it highlights the difficult debate over military commissions currently under way in Congress, which is wrestling with how best to protect national security while also preserving America's tradition of due process and fair trials.

In a series of pretrial motions, Padilla's lawyers argue that information from Mr. Abu Zubaydah and another confidential source used to justify the May 2002 warrant was the product of torture. They say information obtained through torture cannot be used in court and that any evidence seized from Padilla during his Chicago arrest must be excluded from use at his trial.

Padilla fails in bid to exclude evidence

Last week, one day before Mr. Bush publicly acknowledged the secret CIA prisons and interrogations, a federal magistrate judge in Miami rejected Padilla's arguments.

US Magistrate Judge Stephen Brown ruled that defense attorneys had failed to offer enough proof concerning the identity and treatment of the confidential sources the government used to justify the warrant.

In addition, Judge Brown ruled that even if the information the confidential sources provided was the product of torture, defense lawyers had presented no evidence that the FBI agent who prepared the warrant application was aware that they had been tortured. Short of a deliberate effort by that agent to intentionally mislead the court, the defense motion must be denied, the magistrate judge ruled.

Padilla's lawyer, Andrew Patel, says the decision is being appealed to US District Judge Marcia Cooke, the trial judge in the Padilla case. He declined any further comment on the case.

In an earlier brief, Mr. Patel wrote: "The government's claim of ignorance appears either to be incredible or the product of conscious avoidance."

In his speech, Bush justified the harsh tactics as essential to prevent terror attacks. But he also asked Congress to formulate special rules so that Abu Zubaydah and 13 other individuals could be tried by military commissions at Guantánamo Bay, Cuba, despite their harsh treatment while in CIA custody.

The special provisions are necessary, in part, because the US criminal justice system excludes coerced statements as too unreliable to present in court. There is also a blanket ban on information obtained through torture.

Bush insists that torture was not used in the CIA operations. But he declined to identify the specific interrogation practices.

Legal experts say that procedures such as simulated drowning, induced hypothermia, and noise bombardment are highly coercive and can lead subjects to say whatever they think will help stop the harsh treatment. Human rights experts say these kinds of techniques can amount to torture.

Congress debates coercive tactics

The president's public disclosure has prompted a debate in Congress over whether to endorse the CIA's "alternative" interrogation tactics. But Bush is also asking lawmakers to grant retroactive legal immunity to US interrogators who engaged in or were present during these practices. The request is being made despite the president's assurance that they are legal and do not amount to torture.

The government has never acknowledged the identities of the two sources used for the 2002 warrant. Defense lawyers and other analysts identified them by cross-referencing the unique information the sources provided to the government with public sources and documents that matched the same information. In addition to Abu Zubaydah, defense lawyers say the second source used to obtain the Padilla warrant was an Ethiopian named Binyam Mohammed.

Mr. Mohammed is one of 10 individuals being held at Guantánamo Bay who had been facing war-crimes conspiracy charges before the military commission process was struck down by the Supreme Court. Because of those charges, he has been afforded access to a lawyer.

According to an affidavit signed by Patel, Mohammed was being held in Pakistan at the time the Padilla warrant application was prepared. US agents wanted incriminating information about Padilla. The affidavit says Mohammed was hung on a wall with a leather strap around his wrists for a week by his Pakistani jailers. He was beaten with a leather strap, and was questioned with a loaded gun pressing into his chest, the affidavit says.

It says he was questioned by four individuals who identified themselves as agents of the FBI. The affidavit adds that Mohammed says he is sure that if he sees them again or sees their photos he will be able to identify them.

Mohammed has told lawyers that US agents were not happy with his level of cooperation against Padilla and sent him from Pakistan to Morocco. There, according to an Amnesty International report, Moroccan interrogators used a razor blade to make 20 to 30 small cuts on his genitals. This was done once a month for 18 months, the report says. Eventually, Mohammed was sent to Afghanistan and then Guantánamo.

The specific issue in the Padilla case is whether federal prosecutors in Miami can use evidence seized from Padilla at the Chicago airport and use statements Padilla made during nearly eight hours of questioning by customs, immigration, and FBI agents before he was given Miranda warnings and placed under arrest.

After arresting Padilla, agents found the names and telephone numbers of individuals the government says were Padilla's Al Qaeda recruiter and his sponsor. They found the e-mail address of Ammar al-Baluchi, a key aide to Khalid Sheikh Mohammed, the alleged mastermind of the 9/11 terror attacks. And they discovered a cellphone that had allegedly been provided to Padilla by Al Qaeda officials.

In addition, they confiscated $10,526 in cash, most of which they allege had been provided to Padilla by Al Qaeda leaders in Pakistan a month earlier. During questioning, agents say Padilla told them that he received the money in an envelope from an individual in Pakistan, but then said it was money he had earned.

Such evidence could play a critical role in Padilla's terror conspiracy trial, set to begin in January. Judge Cooke has already criticized the government's case as being "very light on facts." She has dismissed the most serious conspiracy count in the indictment.

Evidence: 220 tapped conversations

The bulk of the evidence against Padilla's alleged coconspirators is 220 intercepted conversations. But there are only 28 instances where Padilla speaks or is allegedly mentioned, according to court documents. And none of the 28 conversations directly implicates Padilla in any acts of violence, his lawyers say.

In contrast to the skimpy evidence in the Miami criminal case, the government has assembled a mountain of intelligence information about Padilla's alleged actions and cooperation with Al Qaeda. But virtually all of it was obtained from interrogations during his 3-1/2 years in military detention as a presidentially designated enemy combatant, or through the harsh interrogation of other enemy combatants overseas. As such, it is generally ineligible for use in the criminal court system.

The 2002 warrant issue is important, legal analysts say, because it could lead to wider use in American courts of the fruits of harsh interrogations overseas. And it highlights the difficulty of blending proactive intelligence operations with law-enforcement efforts, these analysts say.

Zayn Abu Zubaydah

He's a Palestinian, born in Saudi Arabia, and the first significant member of Al Qaeda captured – in March 2002 in Pakistan. Intelligence officials say he:

• Headed the reorganization of Al Qaeda in Pakistan, as well as planned attacks on US interests.

• Had connections to a plan to blow up the US Embassy in Sarajevo, the capital of Bosnia-Herzegovina, as well as a planned attack on the American embassy in Paris.

• Is thought to have briefed Richard Reid, the so-called shoe bomber, who was arrested on board a flight from Paris to Miami in December 2001

• Is a master of disguise who used at least 37 aliases

• Is the first Al Qaeda suspect subjected to harsh interrogation, according to President Bush in a speech Sept. 6. He was interrogated in Thailand and initially questioned by the FBI, which gave him some humanitarian aid. A CIA team was later sent in. It apparently forced him to strip and stand in a cold room and subjected him to loud music.